The present invention relates generally to blood filter devices for temporary placement in a blood vessel to capture embolic material, and more particularly to a cannula with a modular filter device for placement in a blood vessel to carry blood to the vessel and to entrap embolic material in the vessel, for example when delivering blood to the aorta from a bypass-oxygenator system during cardiac surgery. The present invention also relates to methods for protecting a patient from embolization which may be caused by procedures, such as incising, clamping and unclamping, which may dislodge atheromatous material from an artery.
During cardiac surgery, it is often necessary to introduce a cannula into an artery or other blood vessel. For example, an arterial cannula is typically introduced into the aorta to deliver blood from a bypass-oxygenator system. Such a cannula generally includes a proximal end for receiving blood from a bypass-oxygenator machine, a distal end for entry into an artery, and a lumen extending between the proximal and distal ends.
One concern with such procedures is that calcified plaque or other embolic material may be dislodged, particularly when clamping or unclamping arteries such as the aorta. See Barbut et al., xe2x80x9cCerebral Emboli Detected During Bypass Surgery Are Associated With Clamp Removal,xe2x80x9d Stroke, 25(12):2398-2402 (1994), which is incorporated herein by reference in its entirety. Such embolic material may travel downstream, possibly becoming lodged in another portion of the blood vessel or possibly reaching a vital organ, such as the brain, where the material can cause substantial injury to the patient.
For this reason, some arterial cannulas may include a blood filter device attached directly to them. For example, an expandable filter device may be mounted on the distal end of a cannula, allowing the filter to capture any loose embolic material once the cannula is introduced into the vessel. Generally, such devices include an expandable frame, such as an inflation seal or an umbrella frame, and a filter mesh attached to the frame, the mesh being adapted to capture embolic material of a predetermined minimum size. The frame may be attached externally to the distal end, or alternatively, it may be retractably deployed from a lumen within the cannula.
The use of a cannula with such a filter device, however, may not be as effective as desired. For example, because the filter is generally attached to the distal end of the cannula, the filter may be exposed within the vessel for the entire duration of the procedure, sometimes several hours. Because of the length of time of most cardiac procedures, the filter mesh may eventually become clogged due to thrombus formation or buildup of embolic material, preventing the device from effectively capturing additional material and/or possibly impairing blood flow through the filter. If the filter is retractable, it may be closed within the vessel when it becomes clogged, but this prevents capture of embolic material throughout the remainder of the procedure.
Accordingly, there is a need for a filter device for use with an arterial cannula that minimizes the exposure of the filter within a blood vessel, thereby reducing the risk of clogging the filter mesh.
The present invention is directed to a modular blood filter device and a delivery system for intermittently introducing the filter device into a blood vessel during an extended surgical procedure, and to methods for using such a device. The present invention is also directed to an arterial cannula with modular filter device for temporary placement in a blood vessel to carry blood to the vessel and to entrap embolic material in the vessel, for example when delivering blood to the aorta from a bypass-oxygenator system during cardiac surgery.
Generally, an embodiment of an arterial cannula with modular filter device in accordance with the present invention comprises a cannula with a side port and a modular filter cartridge, the latter including an expandable filter device and a tubular cartridge. The cannula is an elongate tubular member, having a distal end adapted to enter an artery, a proximal end adapted to receive blood from a bypass-oxygenator machine, and a lumen which extends from the proximal end to the distal end. The cannula also includes a side port for receiving the modular filter cartridge. The side port may be attached to or integrally formed on the outer surface of the cannula, possibly on the front (downstream area), back (upstream area) or side of the cannula. Preferably, the side port is located adjacent the distal end of the cannula, for example above the suture flange thereon. More preferably, the side port extends diagonally from the outer surface to facilitate directing the filter device towards the distal end of the cannula. A passage extends front he side port to the lumen in the cannula, or alternatively, may extend distally from the side port along a wall of the cannula to an outlet on or adjacent the distal end of the cannula. The side port may include a hemostatic valve across the passage to provide a fluid-tight seal, yet allow a modular filter cartridge to be received in and removed from the side port.
An expandable filter device for use with embodiments of the present invention generally includes a semi-rigid shaft having a handle on its proximal end and an expansion frame on its distal end. Filter mesh is attached to the expansion frame to provide an expandable filter capable of assuming enlarged and contracted conditions.
The expansion frame for the expandable filter may be self-expanding upon deployment, or may be controlled from the handle on the proximal end of the shaft. For example, the expansion frame may be formed from a superelastic or shape memory material, such as a Nitinol ring, that opens automatically when deployed. Preferably, the ring includes kinks where the right is attached to the shaft, biasing the ring against the wall of a vessel, and maximizing the cross-section of the vessel intersected by the filter. Thus, once deployed, the ring automatically expands across the vessel, opening the filter, such as a substantially conical mesh, to capture embolic material in the vessel.
Alternatively, the expansion frame may include an annular inflation seal, such as a silicon balloon, that may be filled with fluid to open the mesh across the vessel into which the device is deployed. In this embodiment, the shaft may include an inflation lumen extending between the proximal and distal ends thereof for injecting and removing fluid.
The expansion frame may also be mechanically operated, such as by a guide wire and/or a spring connected to the expansion frame, generally controlled from the handle on the proximal end of the shaft. For example, the expansion frame may include a plurality of struts that may be biased to the contracted condition, possibly using a shape memory material or a spring. A ring attached to the struts may be directed axially to expand and contract the struts respectively between the enlarged and contracted conditions.
In addition, the cannula with modular filter device also includes a tubular cartridge into which the expandable filter device may be inserted. Generally, the cartridge is a tubular member providing a hemostatic seal between the shaft on the filter device and the side port on the cannula, or the cartridge may include a hemostatic valve to provide a fluid-tight seal between the cartridge and the filter device inserted therein. The cartridge generally has a shape similar to the side port, as well as the shaft on the filter device. Preferably, these components have similar cross-sections, such as a substantially square or rectangular shape, that limit the arterial cannula with modular filter device to a predetermined assembled orientation that ensures that the filter device is deployed across the vessel when deployed. The distal end of the shaft on the expandable filter device is generally inserted into the cartridge, such that the expansion frame and mesh are substantially contained within the cartridge, thereby providing a modular filter cartridge.
The modularity provided by the cartridge, combined with the side port on the cannula, is an important feature of the present invention. During use, the cannula may be introduced into a blood vessel, such as the aorta, using conventional procedures, a modular filter cartridge generally being provided in the side port prior to introduction of the cannula. Once the distal end of the cannula is in position within the vessel and the cannula is secured to the patient, the filter device may be deployed into the vessel. The shaft of the filter device is directed distally, causing the expandable filter on the distal end of the shaft to pass through the passage, through the lumen in the cannula and exit the distal end of the cannula into the vessel. The expansion frame may then expand automatically as it enters the vessel, or it may be expanded mechanically to its enlarged condition, opening the filter mesh substantially across the vessel and capturing any embolic material traveling therethrough. At any time, the expansion frame may be closed to its contracted condition, either automatically by withdrawing the expandable filter, or by mechanically closing it as described above, entrapping any embolic material captured by the mesh. The expandable filter may be returned into the cartridge by pulling the shaft proximally, and the modular filter cartridge may then be removed from the side port if desired. A new modular filter cartridge may be inserted into the side port, and a new filter may then be introduced into the vessel.
The ability to replace the filter at any time during a procedure is particularly useful in cardiac surgery. For example, the cannula and filter may be deployed as described above within the aorta. The aorta may then be clamped in preparation for a bypass procedure, possibly dislodging embolic material from the wall of the aorta and traveling downstream. With the filter deployed, however, embolic material released during this action may easily be captured by the filter device. Once the aorta is clamped, the risk of embolic material breaking loose is substantially reduced, and so the filter may be removed without substantial concern about embolic material escaping to other areas of the patient.
Later in the surgery, a new filter may be introduced into the aorta when the risk of embolic material becoming dislodged is again increased, as for example when the aorta is unclamped. Because a new filter may be deployed, any embolic material that is dislodged has a much greater likelihood of being captured by the filter without substantially impairing blood flow through the vessel. Thus, a cannula with modular filter device in accordance with the present invention may more effectively capture and remove embolic material released during extended procedures, such as coronary bypass surgery.
Accordingly, a principal object of the present invention is to provide a modular blood filter device and delivery system that allows the filter to be decoupled from the delivery system when not needed, and that allows a new filter to be introduced to more effectively capture embolic material within the vessel, such as during an extended surgical procedure.
It is also an object of the present invention to provide an arterial cannula with modular filter device that substantially minimizes the likelihood of the blood filter becoming clogged and ineffective during use.